Chirality versus dichroism: Competition and role in conical diffraction displayed from the Nd:Bi2ZnOB2O6 acentric biaxial laser crystal

Abstract We have grown acentric chiral Nd-doped BZBO single crystals by the Kyropoulos method, cut perpendicular to the optical axis. With a focused beam at wavelengths in the spectral domain of transparency with various polarizations, the conoscopy patterns revealed the specific role of chirality: disappearance of the optical axis replaced by two C-directions, linear polarization rotation and spiral patterns. The specific rotatory power was measured. The output near field exhibits the influence of chirality on the conical diffraction. Going to wavelengths in the spectral domain of absorption corresponding to the 4 I 9/2  →  4 F 5/2 Nd 3+ transition, we first studied the chirality/dichroism competition from propagation along the C-directions, characterizing the circular and elliptic eigen-modes. We exhibited the wavelengths at which the ellipse degenerates linearly, signature of the chirality/dichroism balancing. The second aspect is the existence of the optical axis which can be restored if the dichroism is high enough. In this case a singular Voigt wave can propagate. From the experimental determination of the optical parameters, a theoretical description has been proposed, leading to quite well agreement in the far field (conoscopy) and in the near field (conical diffraction).